Problem: $ { {5} \times \left[\begin{array}{r}{-1} \\ {3} \\ {2}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{5}\times{-1} \\ {5}\times{3} \\ {5}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-5} \\ {15} \\ {10}\end{array}\right]}$